#3sqrt(50) - 3sqrt(32)#:
the surds in the question are not simplified. therefore they can be broken down further.
#3sqrt(50)#:
factors of #50#: #1,2,5,10,25,50.#
#sqrt(25) = 5#
#therefore 3sqrt(50)=3*sqrt(25)*sqrt(2)#
#=3*5*sqrt(2)#
#= 15sqrt(2)#
#3sqrt(32)#:
factors of #32#: #1,2,4,8,16,32#
#sqrt(16)=4#
#therefore 3sqrt(32)=3*sqrt(16)*sqrt(2)#
#=3*4*sqrt(2)#
#=12sqrt(2)#
the question is simplified to #15sqrt(2) - 12sqrt(2)#
law of surds:
#asqrt(b) + csqrt(b) = (a+c)sqrt(b)#
#15sqrt(2) + -12sqrt(2) = (15-12)sqrt(2)#
#=3sqrt(2)#